What would make the Catalytic Converter on 1990 Cadillac Deville glow red even after the cat plugs wires and dist cap have been replaced?

When the convertor gets hot enough to glow red, replace it immediately, and also resolve the original cause of the problem! Chances are, your next converter will soon go bad, if the original problem is not fixed.

Catalytic convertors (Cats) normally operate between 800 and 1500 degrees without glowing red. When the convertor gets hot enough to glow red, it is extremely dangerous. It can even burn the rug above it. [Say, This happened to me and caused a fire in my car while I was parked!] God forbid if anything touches the Cat: a plastic bag, dry grass or gas fumes at a gas station. It just is not worth it to ignore such trouble.

. Check to make sure that the plug wires are installed in the proper order. If the plugs are not firing at the right time, this will cause unburned fuel to be sent through the exhaust to the Cat where it ignites, causing the converter to glow.

. According to the Cadillac service manual, this will Glow Red after a few miles of driving if the Converter is faulty or needs to be replaced. -TOM

. One should remove and clean the spark plugs about every 10k miles or so, and remove and replace the spark plugs, ignition wires, distributor cap and rotor approximately every 30k miles. To go much longer than this can, and eventually will, cause the catalytic convertor to become clogged with carbon build up.

. Be sure to ask your technician to check for good exhaust flow. There are four possibles for restricted exhaust flow: 1) The Cat is undersize. You may have replaced the Cat, and they supplied a cheaper model; 2) The Cat became defective, and the matrix collapsed; 3) the Cat or muffler is clogged; 4) one of your exhaust pipes are bent and not letting the exhaust flow correctly. Check the exhaust pipes everywhere for extreme bends, especially the tail pipe.

ANSWER. When a cat get's red hot, there is usually one reason why: Because it is always getting unburnt fuel from the engine, which accumulates (carbon), which ignites and get's charcoal-hot. Almost always, the problem originates upstream of the cat. If the O2 sensor is bad, that can be sending the wrong message to the computer. It can be due to bad plugs or bad timing (but you said you replaced the plugs, wires, distributer cap, etc). The next after those would be the ignition coils.

The next question I would ask is: Does the engine temperature guage show Hot? If so, I would suspect the ignition control module, which has alot to do with engine temperature. Try a used I.C. module from a junkyard to see if it is better (or not). Otherwise, always go with new electrical parts.